In recent years, as concern about environmental pollution has increased, a secondary battery, which can be charged and discharged, has attracted considerable attention as a power source for vehicles in order to solve problems caused by existing gasoline and diesel vehicles using fossil fuel. As a result, electric vehicles (EV), which are operated only using a battery, and hybrid electric vehicles (HEV), which use jointly a battery and a conventional engine. Some of the electric vehicles and the hybrid electric vehicles have been commercially used. A nickel-metal hydride (Ni—MH) secondary battery has been mainly used as the power source for the electric vehicles (EV) and the hybrid electric vehicles (HEV). In recent years, however, the use of a lithium-ion secondary battery, which has high energy density and high discharge voltage, as the power source for the electric vehicles and the hybrid electric vehicles has been attempted. High output and large capacity are needed for such a secondary battery to be used as the power source for the electric vehicles (EV) and the hybrid electric vehicles (HEV). For this reason, a plurality of small-sized secondary batteries (unit cells) are connected in series with each other so as to construct a middle- or large-sized battery pack.
Plate-shaped cells, which can be stacked with high integration, are preferably used as the unit cells. The plate-shaped cells are mounted in additional battery cartridges, in order that low mechanical strength of the plate-shaped cells are compensated for, and the electrical connection and stacking of the plate-shaped cells are easily accomplished, whereby a middle- or large-sized battery module or battery pack is constructed.
The battery cartridges are formed in the shape of a hexahedron having a large width and length to thickness ratio (generally in the shape of a plate). The battery cartridges are constructed in a structure in which one or more unit cells are mounted in rigid cartridge cases. Consequently, the battery cartridges are successively stacked one on another, and are then electrically connected with each other, whereby a middle- or large-sized battery module or battery pack is manufactured.
The middle- or large-sized battery module or battery pack is widely used as a power source for large-sized devices, such as electric vehicles and hybrid electric vehicles. However, the inner spaces of the respective devices, in which the middle- or large-sized battery module or battery pack is mounted, are restricted. Also, as the devices have had various sizes and shapes, the devices may have a structure in which the battery module or the battery pack cannot be easily mounted in the inner spaces of the devices.
On the other hand, the change in shape of a conventional battery cartridge, which constitutes a middle- or large-sized battery module or battery pack, is not possible because of the rigid structure of the conventional battery cartridge. As a result, the conventional battery cartridge is not adaptable to the change in structure of the inner space of the corresponding device. Consequently, it is necessary to manufacture various battery modules or battery packs depending upon the structures of the inner spaces of the devices, and therefore, a large number of corrections, such as design change, are required during the manufacturing process, which is not preferable.